1. Field of the Invention
The invention relates to a carbon fiber, and more specifically to a PAN-based carbon fiber, a fabrication method thereof and a precursor raw material thereof.
2. Description of the Related Art
According to studies by the Department of Energy, USA, if 25% of car materials are replaced with carbon fiber composite materials, fuel efficiency will increase by 30% due to the lighter weight, which will save fuel amount by up to 15% and decrease carbon dioxide emissions by more than 20%. Currently, PAN-based carbon fibers produced by a wet-spinning (solvent spinning) method hold 90% of the world carbon fiber market. Although melt-spinning (non-solvent) PAN-based carbon fibers have competitive advantages of low-cost and environmental friendliness, commercialization thereof has yet to be realized. According to reports by J. A. Davidson, S. R. Hutchinson and T. Mukundann etc., currently, the difficulties of producing carbon fiber precursors from PAN polymers by the melt-spinning method are: (1) if the quantity of co-monomers in the PAN polymer is too low (which means the quantity of acrylonitrile (AN) in the PAN polymer is too high), the spinning process will cause a cross-linking reaction etc., and the fiber breakage rate will be high, wherein the fibers are not able to be rolled successfully; and (2) if the quantity of co-monomers in the PAN polymer is too high (which means the quantity of acrylonitrile (AN) in the PAN polymer is too low), while melt-spinning can be accomplished, however, time will increase during the subsequent high-temperature oxidization reaction of the fiber precursors, which will increase defects, lower yield, and decrease quality of the carbon fiber products. PAN copolymers for ordinary plastics need to have appropriate co-monomer categories and percentages during the melt-spinning process in order to appropriately produce melt-spinning PAN-based carbon fiber precursors and then melt-spinning PAN-based carbon fibers. Currently, the most critical issue needed to be resolved when preparing melt-spinning PAN-based carbon fibers from fiber precursors is the long oxidization process (around more than 20 hours), which increases defects, lowers strength and lowers yield of carbon fiber products. Compared with conventional wet-spinning PAN-based carbon fibers, the problems of melt-spinning PAN-based carbon fibers come from the differences between the composition of the polymer precursors; specifically: a. a high-quantity of co-monomers with low oxidization/cyclization ability, for example methyl acrylate (MA) (around 15 mol %), however, the wet-spinning polymer precursor is around the itaconic acid (IA) (1 mol %) and MA (2 mol %) levels; b. the melt-spinning polymer precursor does not contain the compounds capable of catalyzing oxidization/cyclization, for example acidic itaconic acid (IA), decreasing the ability and rate of oxidization/cyclization.